containing much sulphur is objectionable as a
fuel for enamel stoves Mr. Dickson emphasizes this very forcibly. He
says: "In the days when stoves were heated by coke furnaces, and the
heat distributed by the flues, the principal trouble was the escape of
fumes of sulphur which caused dire disaster to all the enamels by
entering into their composition and preventing their ever drying, not
to speak of hardening. I have known enamels to be in the stoves with
heat to 270 deg. for two and three days, and then be soft. The sulphur
also caused the enamels to crack in a peculiar manner, much like a
crocodile skin, and work so affected could never be made
satisfactory, for here again we come back to the first principle,
that if the foundation be not good, the superstructure can never be
permanent. The enamels, being permeated with sulphur and other
products from the coke, could never be made satisfactory, and the only
way was to clean it all off. The other principal troubles are the
blowing of the work in air bubbles, which is caused mainly by the heat
being too suddenly applied to the articles, but these are very small
matters to the experienced craftsman."

[Illustration: FIG. 6.]

2. _Stoves heated by hot-water pipes._--Let us first of all consider
the principle on which these are constructed. In Perkins' apparatus
for conveying heat through buildings by the circulation of water in
small-bore hot-water pipes an endless tube or pipe is employed, the
surface of which is occasionally increased by spiral or other turnings
where the heat is to be given off or acquired: the annexed figure may
serve to illustrate this principle; it represents a strong
wrought-iron tube of about one inch diameter completely filled with
water; the spiral A passes through a furnace where it is highly
heated, and the water is consequently put into motion in the direction
of the arrows; the boiling of the water or formation of steam is
prevented by the pressure, whence the necessity of the extreme
perfection and strength of the tube. B represents a second coil which
is supposed to be in an apartment where the heat is to be given out. C
is a screw stopper by which the water may be occasionally replenished.
By this form of apparatus the water may be heated to 300 deg. or 400 deg., or
even higher, so as occasionally to singe paper. A larger tube and
lower temperature are, however, generally preferable.[1]

[Illustration: FIG. 7.--Enamelling Stove--in a T